(1) Field of the Invention
The invention relates to a light guide apparatus, and more particularly to the light-guide apparatus which is manufactured by a co-extrusion process and capable of light reflection, distribution and guiding. The light-guide apparatus can integrate an edge light source to perform as a backlight module for display devices.
(2) Description of the Prior Art
A light-guide plate is known to be a light-guide medium for a backlight module of display devices. The light-guide plate can be used as an edge-type module that guides lights emitted by an edge light source to leave vertically from a front surface of the display device so as to enhance the luminance and distribution of the display device.
Theoretically, the light-guide plate is to direct the incident lights to a particular side (usually the front surface) of the plate. The lateral side of the plate can diffuse to reflect the lights back into the plate and to leave from the front surface of the plate. A high refraction index of the plate usually implies a better light-guiding performance. Also, the bottom surface of the light-guide plate is usually formed as a reflection surface to send back lights into the plate and so as to have the light leave the plate at the targeted front surface.
Referred to FIG. 1, a conventional backlight assembly 5 disclosed in a U.S. Pat. No. 7,108,385, filed on Sep. 19, 2006 is shown to have an LCD panel 57, a diffusing membrane 56, a lens module 55, a light source module 50, and a light-guide module. The light-guide module further includes a front surface 523 for leaving the lights, a light-guide plate 520 and a reflection plate 524. The edge-type light source 50 energized and controlled by a circuit board 51 is attached to a lateral side 521 of the light-guide module.
In the art, the backlight assembly like the one shown in FIG. 1 usually has the following shortcomings in individual parts. These shortcomings in parts of the conventional backlight assembly are listed as follows in Table 1.
TABLE 1Shortcomings in parts of a conventional backlightassemblyPartFunctionShortcomingsReflectionTo reflect incident lightsIncreasing the light loss andplate 524back into the light-guidethus reducing the lightplateutilization efficiency by thespacing in between with thelight-guide plateIncreasing the cost of thebacklight assemblyLight-guideTo forward lights fromIll-visibility caused by lineplate 520the edge-type light sourcedefects from the necessaryto the front surfacenetting structureNeeding the diffusingmembrane to cure the linedefectsDiffusingTo homogenize the lightsIncreasing the cost of themembrane 56in the light-guide plate,backlight assemblyand to protect the lensmodule from possiblescratchesLens moduleTo coverage the lights,Increasing the cost of the55 (BEF)and to enhance thebacklight assembly byluminositydifficulties in manufacturingand designVulnerable to break andscratchCausing redundant workingcost in view of the workingin the micro-structure of thelight-guide plate
Referred to FIG. 2, a lateral view of the light-guide plate 520 is shown to elucidate one of the aforesaid shortcomings in light loss of the light-guide plate 520 during a light transmission path. In order to increase the reflection efficiency of the backlight assembly 5, the additional reflection plate 524 is recommended to be included. Because a tiny air spacing 525 is always there between the reflection plate 524 and the light-guide plate 520, a loss in light 581 up to about 8% is inevitable. Such a light loss in between would decrease the light utilization efficiency but increase the manufacturing cost of the backlight assembly 5.
In addition, the light-guide plate in the art can be produced by applying an additional printing process, which involves steps of screen format preparing, inking and screen printing. All these complicated processes may contribute mainly to shortcomings in production yield and glazing bands. As shown in FIG. 3, glazing bands on a conventional light-guide plate 520 is schematically illustrated. These glazing bands may result in non-uniform brightness distribution to the light-guide plate 520; for example, to separate the screen into a bright area 582, a middle area 583 and a dark area 584.
As described above, the air spacing existing between the light-guide plate and the reflection plate can contribute to the increased light loss, the cost hike in producing the backlight assembly, the line defects, the manufacturing difficulty in the lens module and damages to the surface micro-structure. Hence, improvement upon overcoming the air spacing between plates shall be highly expected by the skill person in the art.